1. Field of the Invention
This invention relates to an apparatus for recording an image signal on a recording medium.
2. Description of the Related Art
With the recent progress of recording techniques, video movie cameras in which a video camera and a video tape recorder are combined have been developed as an image signal recording apparatus-capable of recording a digital sound signal along with a moving image signal. In this kind of recording apparatus, a digital still image signal stored in a memory can be recorded on a recording medium such as a magnetic tape simultaneously with the picture taking and recording of a moving image signal by utilizing a recording medium portion for a digital sound signal.
Electronic still cameras capable of recording an optical image of an object by converting the image into an electrical signal are known as another kind of image signal recording apparatus. The size of an image pickup surface of such electronic still cameras is about 13 mm along a diagonal line in the case of a 1/2 inch charge coupled device (CCD) sensor, while the corresponding size of silver salt cameras using 35 mm film is about 45 mm, and the view angle of the former is 1/4 that of the latter. Electronic still cameras can be used more easily and conveniently to record or reproduce images in comparison with silver salt cameras and therefore have come into use, for example, in the building industry for the purpose of taking pictures of circumstances of building sites and in the real-estate business for the purpose of making pictures for use in advertising, presentations and the like.
A still image signal can be recorded comparatively easily with respect to a unit corresponding to a field by using a video movie camera on the basis of a still image signal digital recording method such as that mentioned above, if a brightness signal and two color difference-signals output from an image pickup processing circuit of a video camera section are stored in a memory. In the case of recording a still image signal with respect to a unit corresponding to a frame, only a still image signal obtained by imaging a stationary object can be recorded; a still image signal obtained by imaging a moving object results in a blurred still image.
The size of the imaging surface of CCD sensors used in electronic still cameras is smaller than that of the ordinary imaging surface of silver salt cameras. Therefore, a picture taking lens having a shorter focal length is required, if a view angle wider than that for a portrait photography is required to express, for example, the relationship between a particular working place and the overall circumstances (in the case of the building industry), or an interior design, an overall view of an object or the relationship between an object and an adjacent building (in the case of the real estate business). For example, to obtain the same view angle as with a picture taking lens having a focal length of 20 mm in a silver salt camera, it is necessary for an electronic still camera to have a picture taking lens with a focal length of about 5 mm. In this case, there results a problem of an increase in manufacturing cost or a limitation on reducing the overall size of the camera. Recently, CCD sensors having an imaging surface diagonal line length of 1/3 inch have come into use and, therefore, this problem has become more serious. Moreover, the number of pixels of image pickup devices for use in electronic still cameras is for some purposes not sufficiently large, and there is, therefore, a problem in terms of image quality if a short focal length lens is used in a camera mainly designed for portrait photography.